This invention relates to a repetitive method for making, filling and sealing sacks from a tubular web of thermoplastic material, preferably provided with side folds, wherein, for each sack, the leading end of the tubular web is provided with a transverse weld, and from the tubular web a section constituting an open sack is cut off, and wherein the sack is then filled and the open side of the sack is closed by a transverse weld.
Such methods are known in the prior art. For instance, the sections that will later on constitute the sack are withdrawn from a tubular chain in accordance with a known method. Said tubular chain is perforated at predetermined distances, so that the sections corresponding to the future sack can accordingly be torn off along the perforations. After closing the bottom weld, the individual tube sections are supplied to a charging funnel to be filled for instance with granular material. When a predetermined quantity of the filling material has been filled in, the open sacks are removed, are pulled taut on their open side, and are sealed in a specially provided trimming means.
The generic method can, for example, be carried out by means of an apparatus in accordance with the DEOS 37 15 685. This apparatus comprises sliding and advancing rollers, by means of which successive leading ends of the tubular film web each provided with a transverse weld are intermittently pushed in vertical direction freely hanging down, by one length of bag or sack each, between welding jaws of a welding device, which make opening and closing movements in a horizontal plane. Below said welding jaws a transverse cutting means is disposed, and below said transverse cutting means grippers arranged in pairs on a transport means are provided, which supply the hanging bags or sacks cut off from the tubular film web and provided with bottom welds in horizontal conveying direction via a cooling line for cooling the transverse welds to a transfer means transporting the same to a filling station. The transport means consists of a hub-like supporting member, which is pivotally mounted about a vertical axis, with radial arms at whose free ends the grippers arranged in pairs are provided. The cooling line consists of a cooling carrousel for supplying the sack workpieces, which were provided with the transverse welds and were cut off from the tubular web, from the welding station on a circular path to a means for transferring the sack workpieces to the filling station. When this apparatus comprises, for instance, four radial arms, there is provided above the first station a welding means as well as a cutting means. In accordance with this prior art each cycle of making a sack comprises the steps of introducing from the top a sack already provided with a transverse weld into the first pair of open grippers, and seizing and cutting off the same after it has been advanced by one length of sack. Then, a new transverse weld is formed at the end of the tubular web, while the cooling carrousel intermittently rotates by about an angle of 90.degree. and remains in this position until a further sack provided with a transverse weld has been introduced in the succeeding station. In a four-arm cooling carrousel this is repeated until the first station has rotated by 270.degree. in three cycles. At this point the transverse weld has cooled and the sack is transferred to a transfer means for transporting the sack to a filling station, where after filling the sack a further transverse weld is made for sealing the filled sack, after the open end of the sack has been pulled taut.
In the filling station the sack is filled with a predetermined quantity of filling material, where in general a predetermined weight of filling material is filled in. However, the filling material, for instance a granular material to be filled in, many have different bulk volumes with the same weight. This is, for instance, due to a different moisture content of the bulk material. Due to the different filling levels it can now occur that the sack, after it has been sealed by the transverse weld, has an undesired clearance between the same and the filling material. This means that the sacks are not filled tight, which is in particular disadvantageous in the further handling of the sacks.
This disadvantage is eliminated in the first mentioned method by a corresponding vertical adjustment of the trimming means, which must be made by the machine attendant. This means that the corresponding welding jaws are adjusted in accordance with the current bulk density or the resulting bulk volume of the bulk material. Again, this leads to the fact that in the apparatuses carrying out this method there must always be present a machine attendant for monitoring or adjusting the apparatus.
When carrying out the generic method by means of an apparatus in accordance with the DE-OS 37 15 685 there is in addition the problem that an adjustment of the trimming means disposed in the apparatus is not provided, so that depending on the bulk density of the filling material the sacks are--as desired--filled tight or are, however, filled with an undesired amount of excess air between the filling material and the sealing transverse weld.